Bone conduction hearing device



Oct. 25, 1938. E. H. GREIBACH BONE coNDUcTioN 'HEARING DEVICE Original Filed Nov. 1l, 1935 2 'Sheets-Sheet 1 -.wymfl'l' L1 S mamma u.. (momen AVI/ill n 4 n n n a r r a a ct. 25, 1938. E. H. GREIBACH R12-20,896 j BONE CONDUCTI-ON HEARING DEVICE l Original Filed Nov. 11,' 1935 2 Sheets-Sheet. 2

:inventor M1 SMMPMIZ attorney Rennes oct. 25, 193s :am l f BONE CONDUCTION BEARING DEVICE Emu nem oreibaennrnouyn, N. r. y original No. 2,127,468, aand August 1s, 193s, se-

rial No. 697,673, November 11, 1933. Application for reissue. Beptemberjz, 1938, Serial No.

l49 Claims. (CL 179-101) This invention relates to bone-conduction hearing devices and'it has particular relation to bone conduction `receivers for hearing aids or audiphones. l Among the-objects ofthe invention is a. bone conduction receiver suitable for wearable hearing aids that is small enough for inconspicuous wear in contact with hearing-inducing bones of the user and is powerful enough for imparting to the bones the v ibratory energy required for conducting the sound vibrations Aover the bones of the head to the hearing nerves of the inner ear and induce hearing.

In the bone conduction receiver of the invention a vibratory structure which is setinto vibrations by electric oscillations of the audible frequency range has one o! its vibratory portions coupled to hearing-inducing bones of the user so as to support in a floating condition another vibratory portion having suiiicient inertia and being subjected to suiiicient acceleration for imparting through its inertia reaction vibratory energy to the hearing inducing bones.

In such bone conduction receiver the coupled vibrator-y portion may be utilized to form a protectlve casing around the floating vibratory portion so as to prevent the pressure with which the coupled vibratory portion is held against the bones from aiiectingthe eihciency of the vibratory motion between the iioating and coupled vibratory portions ot the vibratory structure. Such bone conduction receiver may be made in the form of a tiny vibratory casing carrying in its interior the iioating vibratory driving mass portion which is instrumental in producing lthe'inertla reaction hearing-inducing forces trans--` mitted through the casing yto the bone structure.

The foregoing and other objects of the invention will be best'understood from the following o descr'ption o! the exempliiications thereof illustrated in the accompanying drawings in which v Fig. 1 is a diagrammatic view o! a wearable bone conduction hearing aidshowing a boneconduction receiver o! the invention worn on the 45 head of a deafened person; 4

\ F'g. 2 is an enlarged sectional view of a bone conduction receiver exemplifylng the invention;

Figs. 3 and 4v are vertical and horizontal sectional views, respectively, along lines l--I and Fig. 5 is any enlarged sectional view of another bone conduction receiver exemplifying the in' vention;

Figs. 6' and 7 are vertical sectional views. re- 66 spectiveiy, along lines t-l and 'I-l of lig. 5;

Bussum Fig. 8 is an enlarged sectional view oi another bone conduction receiver exempliiying the invention; l

Figs. 9 and 10 are vertical and horizontal sectional views, respectively along line A3---9 and 5 lll-Ill of Fig. 8;

Figs. 11 and 12 are sectional views of other types oi'bone conduction receivers exemplifying the invention.

It has long been known that the majority of 10 the deafened persons have impaired middle ears and can hear muchbetter sound vibrations conducted through the bones of the head to the inner ear than sound transmitted through the air in the ear canal. However, prior to the present inven- 15 tion, only telephone hearing aids which transmitted sound through air in thev ear canal and the middle ear have been available for the deafened. All prior efforts to make a bone conduction hearing device followed the principles underlying 20 the telephone receivers and utilized an externally 'supported 'heavy driving mass of a vibratoryl structure for vibrating a driven vibratory member pressed against the bones. Since the bone structure is hard and not as yielding'as the air, 25 the back pressure .of the bones forced the driven vibratory member against the externally supported heavy driving mass of the vibratory stmolture and brought about operating dimculties. As

a result all prior operative bone conduction hear- 30 ing devices had to be large, heavy and cumbersome.

'I'he invention overcomes these diiculties by 'utilizing 'the principle of preservation ci the center oi gravity of a moving mass system for 35 producing byftheinertia reaction ora driving iioating mass portion ci a lvibratory structure the hearing inducing forces o! small amplitude transmitted to the hard bones of the user by a'driven portion of the vibratory structure which is held 40 pressed against the hearing-inducing bones and carries ina iioating condition the driving vibratory mass portion o! the vibratory In accordance with the invention, a vibratory structure` which vibrates under the actions oi' 45 electric oscillations oi' the audible frequency range has a portion which is held coupled under pressuretohearinginducing bonesoftheusersoas to Support in a floating position a massive portion ofl the vibratory structure which hasa sui- 5o ncient inertia and is subjected to sutilcient accelex-ation for producing by the 'inertia reaction of the floating driving mass the vibratory forces required for impressing on the vibratory portion held against the bones corresponding audioi'requency vibrations which are transmitted through the bones to the inner ear and induce hearing by bone conduction.

'Ihis arrangement. makes it possible to-shape the coupled vibratory portion so that it forms a casing enclosing the iloating Vvibratory portion. As a result, the bone conduction receiver of the invention may be made in the form o! a very small vibrating casing which is held pressed against the hearing inducing bones of the user for securing elcient transmission of the vibratory forces to the bones without affecting `the'efciency oi' the vibratory motion between the driven vibratory casing which is held against` the bones and the interior oatingly carried driving massportionl which imparts to the casing the inertia reaction hearing inducing vibratory forces. 1 A wearable bone conduction `hearing aid equipped with abone conduction receiver exemplifying the principles ofY the invention is shown in Figs. 1 to 4. It comprises a bone conduction receiver shaped in the form of a small vibratingcasing 23 which is held pressed against hearing inducing bones of the user outside the ear canal, for instance. the mastoid bone 22, by a resilient head band 2|, of steel, for instance.-

'I'he casing 2li consists of a rigid base 23 and a rigid cover 24 suitably secured to the base and engaged by the head band 2| so as to press the casing 2|| against the bones 22.

The receiver casing 2li is apart of a vibratory structure formed of an electromagnetic 'vibrating I i runit 30 comprising a'magnetic armature core 3| clamped to the base 23 and carrying on a resilient magnetic armature diaphragm 32 a iloating magnetic core 33 having a central polepiece 34 forming with the adjacent i'ace oi' the armature a small magnetic gap. The vibratory structure is actuated with electric au'dio'irequency current oscillationssupplied through terminal bushings 35` provided in a terminal block extending from the base 23 to the actuating windings'of coil 33 mounted on the pole piece 34 so as to produce a vibratory motion between' the mass vof the oat'- ing core 3 3 and the amature core 3| which forms a part of V,the casing 2li. n

-The oating core 33' has a substantial mass and its inertia resists the vibratory motion. As a result the floating core 33 acts as'a driving memberga'ndg'exertsonthe .armature core' `3| and the casing 23`which is coupled tothe hard bones of the head inertia reaction forces proportional to the iloatingmass and the' acceleration. imparted to it by the electric current oscillation in the windings of the coil 33. Since the ca singl 20 and amature 3| which is clamped to it are in engagement with the bones,l these inertia re'- actioni'orces drive the casing against the hard bones and impress oujthel bones relatively largev Aoscillatory inertia reai,-.tioh` forces o1'V small ampliimpressed on the vibratory structure.

Although the pV ciples'underlymg the bone conduction receiver using anlelsectromagnetic .vi-

brating structure shownl in Figs. 2 to f4,"le'ndsV itself for the construction of bone conduction re-` ceivers actuated by other types ot vibrating-strucf I tures, electromagnetic vibrating structures are particularly suitable, i'or'use inksuvch bone con-V duction receivers because they permit the design ormghly 'emciet Vvibrating smictur'es. with verysmalivmagnetic operatinggaps 'oile'ss than pue thousandth of an inch. Such design assures extremely eficient operation oi electro-magnetic bone conduction receivers, and makes possible the construction of bone conduction receivers of exstandard' wearable hearing aid Worn hidden in i the clothing of the user, by substituting the bone conduction receiver for the air conduction recever without having to resort to special transformers or other accessories required when such bone conduction receivers are constructed with other types oi vibrating structures.

In Fig. 1 is shown how the electro-magnetic inertia reaction bone conduction receiver of the invention is connected in the operating circuit of a. prior-art vwearable hearing aid. A conventionally illustrated microphone transmitter 40 is connected in series with a supply battery 4| and a cut-off switch 42 to the actuating coil 43 of a conventionally illustrated amplifier microphone 44 which is connected in series with the battery 4| and-.the cut-off switch 42 by way of a rheostat 45 to the leads 46 whlchhave terminal plugs engaging theterminal bushings 35 on receiver casing and lead to the actuatin`g,winding 36 of the receiver.

With such wearable hearing aid assembly, sound waves of the principal audible frequency range, or the frequency range oi intelligible speech. impinging on the microphone transmitter 4|| willproduce in the primary circuit including the amplier winding 43 corresponding electric energizing coil 36 of the bone conduction receiver which is held pressed against the bones and transmits through the bones corresponding inertia reaction hearing inducing vibratory forces to the inner ear of the user, or his auditory center.

The actual size of the bone conduction receiver shown in Figs. 2 to 4 is only about onethird the size in which it is shown in the original drawings.y Its floating core 33 is formed of a which Athe core piece 34 vis joined of opposite polarity.

Theend surfaces ofthetwo youter core arms of the iloating core33 havetheir outer surfaces on the same level as the pole race of the central core 34, their surfaces-being preferably. ground to the same level. The armature diaphragm 32 is made .of va magnetically `conducting spring steel and has its center portion stiflened by integrally uniting it, as by soldering or brazing,-to a heavy rigid anchoring cross bar 5| of iron, for instance, extending transversely across the diaphragm 32.

The central portion o1 the armature diaphragm 32 extends over the i'ull length 'ofthe cross bar 5|' vand is integrally united thereto as by soldering or'brazin'g. The center portion o! the anchorvbar 5| is provided with a:` threaded hole 2|3 in which is threadedly mounted the armaturecore `3| having- 'atits exterior end a slot for turning it to adjust the distance of its pole face from the pole face of the corepiece 3l.

I'he end portions vof the cross bar 5| are undercut and fit the side walls of a groove provided in may be locked in place, for instance, by a lock member B. To the ends of the armature diaphragm 32 are united, as by soldering or bra'zing, reinforcing plates 51 so as to provide a solid clamping joint between the arms of the floating core 33 andthe ends of the armature diaphragm 32.

However, the gap adjustment may be made before the armature supporting bar 5| is clamped to the base and the base may be made with a solid outer surface. l

The headband 2| has a detachable universal joint connection with the cover 24. A socket 58 with a lock spring 55 arranged similar to a familiar snap fasteneris embedded in the wall of the cover 24, and a shank 60 extending from the head band has a ball-shaped end which may be inserted into the socket to form with it a detachable universal `joint connection. This universal joint connection assures that, when the head band 2| presses the receiver casing, against the bones, the contact surfaces. of the receiver will automatically adjust itself to secure an efficient coupling engagement with the bones.

Instead of a head band, any other suitable ar# rangement for coupling the receiver structure to the bones may be used.

In manufacturing the bone conduction receiver of Figs. 2 to 4, the floating core 33 with the coil 36 and the armature diaphragm 3|-32 with the cross bar 5| may be assembled as a self-contained unit and the gap between the amature 3| and the core piece 34 adjusted by turning the armature 3| until its pole face contacts with the core piece 3l. Thereupon the armature 3| is turned back on its thread until a magnetic gap of the desired small length is provided between the adjacent pole surfaces and the armature 3| is locked in place. In this adjusted position the assembled vibrator structure may be tested and after final adjustment clamped to the base 23.

A practical bone conduction receiver constructed as shown in Figs. 3 to 4.1with the following principal-dimensions, will give satisfactory results: Permanent magnetcore v.of a total outer length of 1"; a core thickness of V."; a core height of about VN; a core width of about a center core diameter of about .120"; and

a diaphragm thickness ofabout .014". The mag'- netic gap is of the order of one thousandth of an inch. `The oating permanent magnet core and the center core of the dimensions given above, have a mass of about 8 grams. The foregoing data show that a satisfactory bone conduction receiver of the invention, suitable for inconspicuous wear by. the user, may be constructed to have an overall volume which is only a fraction of three cubic inches, while utilizing an' efficient magnetic vibrating structure operating with a gap of less than ten thousandths of van inch` and a floating driving mass of more than four grams.

Because of the relatively large maas of the head, the coupled portion of the receiver will under the action of the vibratory forces have only an imperceptible vibratory movement and will be practically stationary. As a result of this vibratory movement, relatively large reactive forces will be imparted by the mass of the floating core to the bones of the head,V transmitting thereto vibrations of small amplitude and large force sufficient to convey; by'bone-conduction speech and music to the auditory center of the head. The magnetic gap is made very small, of

the order of a'mil or less, thereby securing a high negative stiffness and eflicient vibrations. The armature diaphragm32 is made of suiiicient cross section to permit flow of a strong permanent flux through the ga'p and also to permit inducing strong alternating fluxes' through the magnet gapy by the action of the sound-frequency current oscillations passing through the actuating coil. 'Ihe thickness of the'armature -diaphragm is made large enough to yovercome the negative stiffness and secure stable vibrations under the action of the fluctuating magnetic field in the gap.

By making the joint between thevdiaphragm 32 and the bar 5| by which it is held clamped to the base solid and firm, as by soldering, the center portion of the diaphragm strip does-not participate in the vibratory movement of the lateral diaphragm portions, eliminating distortion that might occur otherwise. By providing at thev ends of the diaphragm 32 reinforcing strips 51 which. are integrally united with the diaphragm, disturbances due to non-uniform clamping of the diaphragm ends are prevented, eliminating distortion.

The high negative sti'ness secured by the small magnetic gap enables the use of a relatively thick diaphragm 32 having suicient cross section for carrying the flux while at the same time making its effective stiffness opposing the negative magnetic stiffness sumciently small to operate with a resonance frequency at which good response is secured over a largesound-frequency range.

In the electromagnetic bone conduction receiver described -in connection with Figs. 2 to 4, the relatively large floatingly mounted vibratory mass of the receiver'is utilized to produce tromagnetic vibrating structure with an ex.

tremely small magnetic gap' distanceat which the high flux densities and large magnetic forces in the gap do not produce fringing or freezing of the pole faces bordering the gap. Such small gaps are made possibleby the utilization of the coupled vibratory portion of the vibrating structure as casing whichprotects the floating mass against any disturbance by external forces. This combination of elements assures an extremely efficient vibratory structure and makes possible the development of relativelyl large power in a very small receiver unit.

In Figs. 5 to 'i is shown a bone conduction receiver of the invention constructed with a cantilever-type vibratory structure for producing the inertia reaction forces required for inducing hearing by bone conduction. It` comprises a vibratory casing, formed of a rigid base 'Il and a cover 1I, held pressed against hearing indu ing bones 22 by a head band 2| engaging a channel member formed in the cover 1l. 1li- 1I is a part o! a vibratory structure of the cantilever-type Iormedof a U-shaped permanentv magnet core 12 atingly supported by a sprin`g13 clamped to a block'1l extending from a the base 10, and pole pieces 15 extending from Since the oating c'ore 12 has a substantialv mass and the gap formed between its pole pieces 15 and `rthearmature 16 is very small, relatively large inertia rection forces will be exerted by the floating core l2 .on `theV armature .16 and therethrough over the casing tothe bones for inducing hearing by bone conduction.

In' order to secure eilicient operation of the vibratory structure with a very tiny gap of the order of one thousandth of an inch or less,.the spring 13 ha`s a longitudinal slot for permitting adjustment of the position of the floating magnet core 1 2 Lon the spring 'I3 so as to assure operation at a minimum. gap distance between the pole faces of the vpole pieces 15 and the armature 1E without causingi'ringing oi the adjacent pole faces.

In Figs. 8-10 is shown a bone conduction receiver embodying a balanced magnetic vibratory structure for producing the inertia redaction hearing-inducing vibrations.

It comprises a vibratory casing formed of a I ba'se 80 and' a"cover8l heldpressed against hearing inducing bones 22 by va head band 2| having a universal Joint connectionv with the cover 8i, as in the bone receiver of Figs. 2 to 4. The casing Bil-8| is a part oi' ay vibratory structure formed of a magnetic armature core 82 having its opposite ends vclamped tov two base projections B3 and carrying 'on its magnetic'- diaphragm extensions u a iloating balanced magnetic core system formed ot magnetic core blocks 81 andfcore bars i5 having Acentral core pole pieces B6 facing the opposite faces of the arma-y ture 82 to form therewith two magnetic gaps.

The magnetic system'is mag'netized so that the two pole pieces II are o'i' opposite polarity and pass a permanent magneticilux from 'one pole piece B6 across the amature I2 and its twogaps to thether -pole piece I8, the vpath oi' the permanentflux being completed by themagnetic core' blocks `I l1 through vwhich the ends ofthe opposite magnet bars II' are clamped to the rinforced endsjof the diaphragm B4 without using the diaphragm extensions` Il ior carrying the permanent-linx.` i A A 1 On each pole "piece 8l are mounted coils 'of actuating windings B8 which are supplied with electric""audioirequency oscillations through ter- 'minaiBushings' 89 mounted 'on' a terminal block yeite'nding' from the ybase Il. 'The two coils 88 are `sf;nn'ecte'd that 'when' actuated by audioire- Vq'u'eric'y current oscillations the iiuxin' one magneticga'p' reduced whiie-it is increased in the other. gap, the diaphragm extensions 84 serving fb asfreturnlpaths for the alternating flux. .Since :(5 th' 'farmturen isrigidly clamped fto'the base,

The casing III, the audiofrequency iiux variations in the two armature gaps will produce a vibratory motion between the floating core bars 85 and the armature 82 and the inertia reaction of the iioating mass will exert on the armature I2`, and

therethrough, by way of the casing wall, on the which on the exterior threaded ends of the core pole l V .pieces 86 permit locking of the pole pieces 86 in their adjusted positions.

By using a`balanced magnetic system in the boneconduction receiver of the invention, poi' the type shown in Figs. 8 to 10, even harmonic distortion is eliminated and objectionable saturation of the ilux paths is avoided. x

Since the permanent ux actingon the oppo'- site pole faces of the armature is balanced, the armature diaphragm is not subjected toany perl manent deflection. Furthermore, the maximum amplitude of the vibrations between the armalture and the floating core is limited by the small magnetic gaps of the order of one thousandth of' an inch-on the opposite sides of the armature.

Accordingly, exing of the armature dia- `l phragm beyond its elastic limit is prevented, andV even if the receiver is dropped; and the momentum ofthe heavy floating mass tends to impari:v

a large deflection to the armature diaphragm, this deflection will be limited by the smallgaps on the opposite sides of the armature to a lvalue atwhich the' elasticity of the diaphragm will automatically restorethe normal gap spacing.

out damage, and it may be operated with smaller gaps `than receivers withoutbalanced magnetic v which has a central pole face forming a magnetic gap with the pole face of the ,core piece 92. II'he vibratory structure is actuated by a coil mounted on-.the core piece 92 clamped to thetop 9i oi the casing. to produce under the action o! audiofrequency currents a vibratory motion between the iioating core 94 andthe core piece 92.. As a `result, the inertia reaction of the. oatingcore exerts hearing inducing vibratory forces on the core :piece l2 and. therethrough, over the casing lll'on the hearing-inducing bones engaged bythe casins.

'Ihe casing of the boneconduction receiver shown in Fig. 1-1, is illustrated inthe form of a Abridge -member of a spectacle frame and its exterior walls are .shown curved .to -form a concave contact surface ior'securing intimate coupling engagement with the bones. 22 of the nose and secure an eilcient ion oi the hear- As a result, the receiver may be dropped withfus yas

ing-inducing vibratory energy from the receiver casing to the bones. 1 l

In the arrangement; of Figvv12 is shown an inertia reaction bone conduction receiver of the invention having an electromagnetic vibrating structure similar to that shown in Figs. 2 to 4. It Icomprises a floating magnetic core 33 carried by an amature diaphragm 32 which is clamped to a wall of an enclosing casing 95 having a pro- 10 Jecting contact member 91 with acurved concave contact surface held in engagement with hearing inducing bones 22 of the user. 'lhis bone conduction receiver is likewise designedfor mounting in a bridge member of a spectacle frame 98 forming ahousing around the receiver casing 96 and supporting 'it between two springs 99 so as to prevent the inertia reaction vibrations of the receiver casing 96 which are transmitted by the contact member 91 to the bones of the nose from being transmitted to the spectacle frame 98.

The perfomance and the quality of the reproduction in the bone conduction receivers of the invention described above may be increased without increasing their weight and size by employing instead of ordinary steel diaphragms special may b'e given a relatively greatrthicknesswithout unduly increasing theirfstiifness, thus providing a large cross section of highly permeable magnetic l 1.In a bone conduction hearing aid device suitable for inconspicuous wear by a deafened person, a. vibratqry mstructure comprising a driven magnetic core portion having a contact surface arranged to be held coupled under pressure to hearing inducing bones of the user outsidev the` ear canal, and a driving floatingly carried magneticJ-core portion resiliently joined to said driven coreportion to form therewith a magnetic ux path including a gap, and means for actuating said vibratory structure with electric oscillations `substantially throughout the speech frequency range to produce corresponding vibrations of saidI 1'0 com members across said gap, said vibratory structure and its several parts being so designed andproportioned that at an overall size of the vibratory structure having a volume of less than about three cubic inches, the driving core portion 75 has a sufllciently large mass and exerts under materials of high magnetic permeability, such as` ingly reduce the ilux reluctance and enable de- By using such materials. for diaphragms, they A the action of the electric oscillations suiiicient inertia reaction forces upon said driven core portion and therethrough" upon the coupled bones for imparting theretov the vibratory energy required for conducting corresponding vibrations through the bones. to the inner ear and induce .intelligible hearing;

2. In a bone conduction hearlngdevice suitable for inconspicuous Wear by a userfa vibratory "structure comprising an elastically deformable magnetic core member forming a magnetic flux path including a gap, said core member Ihaving aydriven core portion with a contact surface arranged to be held coupled under pressure to hearing inducing bones of the user and a driving core portion iloatingly carried relatively to said driven core. portion, land windings interlinked with said ilux path for actuating said vibratory structure with electric oscillations of the principal audible frequency range to produce corresponding vibrations of said core" portions across said gap, said driving core portion having a sufllciently large mass and exerting under the action ci the electric oscillations sufllcient inertia reaction forces through said contactv surface upon the coupled bones for imparting thereto the vibratory energy req red for conducting corresponding vibrations through the bones to, the inner ear and induce intelligible hearing.

3. In a bone conduction hearing device suitable for incqnspicuous wear by a user, a' vibratory structure having a driving magnetic core member and a driven magnetic core member resiliently'joined into a magnetic flux path including a gap, means for holding said driven core member coupled under pressure to hearing inducing bones .of the user outside -the ear canal and carrying said driving core member in a floating condition, and windings interlinked .with said ux path for actuating said vibratory structure with electric v oscillations of .the principal audible frequency range to produce corresponding vibrations of said core members across said gap. said driving core member having a sufciently large .mass and ,exerting under the action of the electric oscillations suflicient inertia reaction forces upon saidv driven core member and therethrough upon the coupled bones for imparting thereto the vlbratory energy required for conducting corresponding vibrations through the bones to the inner ear and induce intelligible hearing.

4. In a bone conductionl hearing aid device suitable for inconspicuous wear by a deai'ened person, 'a vibratory member comprising two resiliently joined magnetic core portions forming a magnetic flux path including a gap, one of said core portions having a rigid contact surface element arranged to be held coupled under pressure to hearing inducing bones of the user andv through the bones to the inner ear and induce intelligible hearing, the sti'ness ofthe resilient junction between said core portions being suiilciently larger to secure a vibratory motion of said core portions at a gap spacing of less than four thousandths of an inch without fringing of said gap.

5. In a bone conduction hearing aid device suitable for inconspicuous wear by a deafened person, a vibratory member comprising two resiliently joined magnetic core portions forming a magnetic flux pathincludinga gap, one of said core portions having a rigid contact surface element arranged to be held coupled under pressure to hearing inducing bones of the user and' oatingly carrying another of said core portions, and means for actuating said vibratory member with electric oscillations substantially throughout the speech frequency range to produce corresponding vibrations of said core portions across said gap, said fioatingly carried core portion having a sufciently large mass and exerting under the action of the electric oscillations sufficient inertia, reaction forces upon said contact surface element and therethrough upon the coupled bones for imparting thereto the vibratory energy required for conducting corresponding, vibrations through the bones to the inner ear and induce intelligible hearing, the stiffness of the resilient junction between said core portions being sumciently large to secure a vibratory motion of said core portions at a gap spacing of less than four thousandths of an inch without fringing of said gap, said contact surface element being arranged and shaped to protect said floatingly carried core portion against external forces.

6.- In a bone conduction hearing device suitable for inconspicuous wear by a user, a vibratory structure having a driving magnetic core member and a driven magnetic core member resiliently joined into a magnetic flux path including a gap, said driven core member having a contact'surface arranged to be held coupled under pressure to hearing inducing bones of the user outside the ear canal, said driving core member being floatingly carried relatively to said driven core member, and windings interlinked with said flux path for actuating said vibratory structure with electric oscillations of the principal audible frequency range to produce corresponding vibrations of said core members across said gap, said vibratory structure and its several parts being so designed and proportioned that at an overall size of the vibratory structure having a volume of less than about two cubic inches, the driving core member has a suiiciently large mass greater than about four grams and exerts under the actionof the electric oscillations sufficient inertia reaction forces upon said driven core member and therethrough upon the coupled bones for imparting thereto the vibratory energy required for conducting corresponding Avibrations through the bones to the inner ear and induce intelligible hearing, said driven core member being arranged and shaped to protect said driving core member against external forces.

'7. In a bone conduction hearing device suitable for. inconspicuous wear by a user, ya vibratory structure havinga driving magnetic corev member and a driven vmagnetic core member resiliently joined into amagnetic flux path including a gap, means for holding said driven core member coupled under pressure to hearing inducing bones of the user outside the ear canal and carrying said driving core member in a floating condition, and windings interlinked with said flux path for actuating said yibratory structure with electric oscillations of the principal audible frequency range to produce corresponding vibrations of saidcore members across said gap, said driving core member having a sufficiently large mass and exerting under the action of the electric oscillations sumcient inertia reaction forces upon said driven core member and therethrough upon the coupled bones for imparting thereto the vibratory energy required for conducting corresponding vibrations through the bones to the inner ear and induce intelligible hearing, said driven core member being arranged and shaped to protect said driving core member against external forces.

8.V In a bone conduction hearing aid device suitable for inconspicuous wear by a deafened person, a vibratory member having two resiliently joined magnetic core portions forming a magnetic flux path including a gap, one of said core portions forming part of a casing having a Contact surface arranged to be held coupled under pressure to hearing inducing bones of the user and floatingly carrying another of said core portions within said casing, and means for actuating said vibratory member with electric oscillations substantially throughout the speech frequency range to produce corresponding vibrations of said core portions across said gap, said floatingly carried core portion having a suiiiciently large mass and exerting under the action of the electric oscillations suilicient inertia reaction forces upon said casing and therethrough upon the coupled bones for imparting thereto the vibratory energy required for conducting corresponding vibrations through the bones to the inner ear andinduce intelligible hearing.

9. In a bone conduction hearing device suitable for inconspicuous wear by a user, a vibratory structure comprising a driven magnetic core member forming part of a casing having a contact surface arranged to be held coupled under pressure to hearing inducing bones of the user outside the ear canal and a driving floatingly carried magnetic core` member resiliently joined to said driven core member within said casing to form therewith a magnetic ux path including a gap, and windings interlinked with said flux path for actuating said vibratory structure with electric oscillations of the principal audible frequency range to produce corresponding vibrations of said core members across said gap. said vibratory 9 V 10. In a bone conduction hearing device suit-w able for inconspicuous wear by a user, a vibratory structure having av driving magnetic core member and a driven magnetic core member resiliently joined into a magnetic flux path including a gap, said driven core member forming a part of a rigid casing having a contact surface arranged for coupling under pressure to hearing inducing bones of the user outside the-ear canal, said driving core member being floatingly carried relatively to said driven core member within said casing, andwindings interlinked with said flux path for actuating said vibratory structure with electric oscillations ofthe principal audible frequency rangev to proaction of-the electric oscillations sumcient inertia duce corresponding vibrations of said core members across saidgap, said vibratory structure and its several parts being so designed and proportioned that at an .overall sire of the vibratori' structure having a volume of less than about three cubic inches. the driving core member has a sufficiently large mass oi the order of eight grams or more and exerts under the action oi' the electric oscillations sufiicient inertia reaction forces upon said driven core member and therethrough upon the coupled bones for imparting thereto the vibratory energy required for conducting corresponding vibrations through the bones to the inner ear and induce intelligible hearing.

11. In an inconspicuous bone conduction hearing device, a vibratory structure comprising a rigid vibratory casing having an external contact surface arranged for coupling under pressure to hearing inducing bones of the user and a driven reaction forces upon said casing and therethrough upon said bones for imparting thereto vibratory energy required for transmitting corresponding vibrations through the bones to the inner ear of the user and induce intelligible hear- 12. In an inconspicuous hearing imparting del vice, a vibratory structure comprising a rigid vibratory casing having an extended external vibration transmitting surface and a driven magnetic core portion operatively exposed to the interior of said casing, a driving magnetic core por- `tion resiliently carried in a `floating condition within said casing to form with said driven core portion a magnetic flux path .including a gap, and means for actuating said vibratory structure with electric oscillations of the principal audible frequency range to produce corresponding vibrations of said core members across saidgap, said floatlngly carried magnetic core portion havingv a mass sufilciently larger than vthe mass of said casing and `exerting under the action of the electric yoscillations sufllient inertia reaction forces upon said casing forimparting thereto vibratory energy required for transmitting from the external surface of said casing corresponding vibrations to the inner earof the user and induce intelligible hearing. s

1`3.In a bone conduction vhearing device suitable for inconspicuous wearby a user, a vibratory .structure having a driving magnetic core member and a driven magnetic core member resiliently joined into a magnetic flux path Aincludingal gap, means including a tor holding said driven core member coupled under pressure to hearing inducing bones of the user outside the ear canal and carrying said driving core member in a `iioating condition within said casing, and windings interlinked with said nux path for'actuating said vibratory structure with electric oscillations of the principal audible frequency range to produce l corresponding vibrations of said core members across said sin, said drivingcore memberhaving a suiliciently large mass and'exerting under the reaction forces upon said driven core member and therethrough upon the coupled bones for imparting thereto the vibratory energy required for conducting corresponding vibrations through thebones to the inner ear and induce intelligible hearing, y

14. In a bone conduction hearing device suitable for inconspicuous wear bya user, a vibratory structure comprising a driven magnetic core member forming part of a casing having a contact surface arranged to be held coupled under pressure to hearing inducing bones of the user,

and a driving floatingly carried magnetic core member resiliently joined to said driven core member within said casing to form therewith a -magnetic flux path including a gap, and windings inter-'linked with said flux path for actuating said vvibrratory structure with electric oscillations of the principal audible frequency range to produce corresponding vibrations of said `core members across said gap, said driving core member having a suiliciently large mass and exerting under the action of the electric oscillations suillcient inertia reaction forces upon said driven core member and therethrough upon the coupled bones for im`- parting thereto the vibratory energy required for conducting corresponding vibrations through the bones to the inner ear and induce intelligible hearing, the stillness of the resilient junction between said core members being sufilcientlylarge to secure a vibratory motion of said core members at'a gap spacing of less than four thousandths of an inch without fringing of said gap.

15. In a bone conduction hearing aid device suitable for inconspicuous wear by a deafened person, a vibratory structure having a driving magnetic core member and a driven magnetic -core member resiliently joined into a magnetic ux path including `a gap, said driven core member forminga rigid casing having a contact surface arranged to be heldf coupled under pressure to hearing inducing bones of the user outside the l ear canal, .said driving core member being. ilo'atingly cz "led relatively to said driven core member within said casingand windings interlinked with said viiux path for actuatng said vibratory structure with electric oscillations substantially lthroughout the speech frequency range to producecorresponding vibrations of said core members across said gap, said vibratory structure and its several parts being s o designed and proportioned that at an overall size oi the vibratory structure having a'volume of less than about two cubic inches and a magnetic gapA spacing of less than about ten thousandths of an inch, the driving core portion has a sufilciently large mass of the' order of eight `grains or more and exerts under the action of the electric oscillations sufiicient inertia reaction forces upon said driven core member and therethrough upon the coupled bones .for imparting thereto the vibratory energy rcquired ior conducting corresponding vibrations through the bones to the inner ear and induce intelligible hearing.

" 16. In a bone conduction hearing device `suitable for inconspicuous wear by anser, a vibratory structure comprising a driven magnetic core member forming part of a casing having a contact surface arranged to be held coupled under pressure to hearing inducing bones of the user :and a driving iioatingly carried magnetic core member resiliently joined to .said driven core member within said casing to form therewith a magnetic iluxpath including a gap, and means bones for imparting thereto the vibratory energy,

required for conducting corresponding vibrations through' the bones to the inner ear and induce intelligible hearing, the stiffness oi' the resilient junction between'said core Vmembers being -sui'- ciently large to secure a vibratory motion of said core members at a gap spacing oi the order of one thousandth of an inch without fringing of 17.' In a bone conduction hearing aid device suitable for inconspicuous wear by a deafened person, a vibratorystructure having a driving magnetic core" member and a driven magnetic core member reslliently joined into a magnetic flux path including a gap, said driven core member forming a rigid casing having a contact surface arranged to be heldA coupled under pressure to hearing inducing bones of the user outside the ear canal, said driving core member being iioatingly carried relatively to said driven core member'within said casing, and windings interlinked with said iiux path for actuating said vibratory structure with electric oscillations substantially throughout the speech frequency range to produce corresponding vibrations of said core members across said gap .said driving core member having a mass `suiiliciently larger than the mass of said driven core member and exerting under the action of the electric oscillations sufficient inertia reaction forces upon said driven core member-' and therethrough upon the coupled bones ior imparting thereto the vibratory energy required for conducting corresponding vibrations through the bones to the inner ear and induce intelligible hearing, the stiffness of the resilient junction between said-core members being sutilciently large to secure a vibratory motion of said core vmembers vat a gap spacing of the order of one thousandth of an inch without fringing of said gap.

18. In a bone conduction lhearing' device suitable forj inconspicuous wear by a user, a vibratory structure comprising a driven magnetic core member'forn'iing part of a casing having a contact surface arranged to be held coupled under pressure to hearing inducing bones of the user outside the ear canal and a driving iloatingly carried magnetic core member resiliently joined to said driven core member within said casing to form therewith a magnetic flux path including a gap, and windings interlinked with said driving core member for actuating said vibratory structure with electricv oscillations of the principal audible frequency range to produce corresponding vibrations of said' core members across said gap, said vibratory structure and its several parts being so designed and proportioned that at an overall size of the vibratory structure havinga volume of less than about three cubic inches and a magnetic gap spacing required for good operating emciency, the driving core portion has a sumciently large mass and exerts under the action of vthe electric oscillations suiiicient inertia reaction forces upon said driven core member and therethrough upon the coupled bones for imparting thereto the vibratorywenergy required for conducting corresponding vibrations through the 19. In abone conduction hearing device suitable for inconspicuous wear by a user, a vibratory structure comprising a driven magnetic core member'iorming part of a rigid 'casing having a -contact'suri'acearranged to be held coupled under pressure to hearing inducingfbones of the user, and a driving iioatingly carried magnetic core member resiliently joined to said driven core member within said casing to form therewith a magnetic iiux path including la gap, and windings interlinked with said driving core member for actuating said vibratory structure with electric oscillations of the principal audible frequency range to produce corresponding vibrations of said core members across said gap, said driving core member having a suiiiciently large mass and exerting under the action of the electric oscillations suilicient inertia reaction forces upon said driven core memberand therethrough upon the coupled bones for'imparting thereto the vibratory energy required for conducting `corresponding vibrationstbrough the bones to the inner ear and induce intelligible hearing, the stiffness of the resilient junction between said core members being suillciently large to secure a vibratory motionof said core members at a gap spacing of less than four thousandths of an inch without fringing oi said gap.

20. In a bone conduction hearing device suitable'for inconspicuous wear by a user, a vibratory structure comprising a driven magnetic core member forming part of a casing having a contact surface arranged to be held coupled under pressure to hearing inducing bones of the user .outside the ear canal and a driving floatingly carried magnetic core member resilientlyjoined to said driven core'member within said casing to form therewith a magnetic iiux path including a gap, and windings interlinked with said driving core member for actuating said vibratory structure with electric oscillations of the principal audible frequency range to produce cor-A responding. vibrations of said core members across said gap, said vibratory structure and/its several parts being so designed and proportioned that at an overall size of the vibratory' structure having a volume of less than about twof cubic inches and a .magnetic gap spacing of less than about ten thousandths' of 'an inch, the

driving core portion has a suiliciently large mass greater than about four grams and exerts under the action of the electric oscillations su'iilcient inertiak reaction forces upon said driven core member Yand therethrough upon the coupledbones for imparting thereto the vbratory energy required for conducting corresponding vibrations throughthe bones to the inner ear and induce intelligible hearing.

-21. Inf a bone conduction hearing device suit-- able for inconspicuous wear by a user, a vibratory structure comprising a driven magnetic core member forming part of a Vcasing having a contact surface arranged to be held coupled under pressure to hearing inducing bones of theuser rand a drivingoatingly carried magnetic core member resiliently joined to said driven core member within said casing to form therewith -a magnetic ilux path including a gapand windings interlinked with said driven core member for actuating said vibratory structure with electric oscillations of the principal audible frequency vrange to produce correspondingvibrations of said lcome core members across said gap, said driving core member having a sufflciently large mass and exerting under the action of the electric oscillations suiilcient inertia reaction forces upon said driven core member and therethrough upon the coupled bones for imparting'thereto the vibratory energy required for conducting corresponding vibrations through the bones to the inner ear and induce intelligible hearing, the stiffness of the resilient junction between said core members being sumciently large to secure a vibratory motion of said core members at a gap .spacing ofless than four thousandths of an inch without fringing of said gap.

22. In a bone conduction hearing device suit-l able for inconspicuous wear by a user, a vibratory structure comprising a driven magnetic core member forming part of a rigid casing having a contact surface arranged to be held coupled under pressure to hearing inducing bones of the user outside the ear canal, and a driving floatingiy carried magnetic core member resiliently joined to said driven core-member 'within said casing to form therewith a magnetic iiuxv path including a gap, and windings interlinked with said driven core member for actuating said vibratory structure with electric oscillations of the principal yaudible frequency range to produce corresponding vibrations of said core members across said gap, said vibratory structure and its several parts being so designed and proportioned that at an overall size of the vibratory structure having a volume of less than about three cubic inches and a magnetic gap spacing required for good `operating eiliciency,y the driving core portion has a sufficiently large mass and exerts under the action of the electric oscillations A sufficient inertia reaction forces upon said driven core member and therethrough upon vthe coupled ,bones for imparting thereto the vibratory energy required for conducting corresponding vibrations through the bones to the inner ear and induce intelligible hearing.

23. In a bone conduction hearing device suitaudible frequency range to produce vcorresponding vibrations of said core members across saidl gap, said vibratory structure and its several parts being so designed and proportioned that at an overall size of the vibratory structure having a volume of less than about three cubic inches and a magnetic gap spacing of less than about ten thousandths of an inch, the driving core member has a sufficiently large mass greater than about four grams of the mass of the vibratory structure and exerts under the action of the electric oscillations suiicient inertia reaction forces upon said driven core member and therethrough upon the coupled bones for imparting thereto the vibratory energy required for conducting corresponding vibrations through the bones to the inner ear and induce intelligible hearing.

24. In a bone conduction hearing device suitable for inconspicuous wear bya user, a vibratory structure having two resiliently Joined core portions forming a magnetic flux path including two gaps, one of said core portions having two surfaces on opposite vsides of said one core p ortion forming pole faces for said two gaps, the other core portion having two pole surfaces facing said pole faces on opposite sides of said two gaps, and ywindings interlinked with said flux path of actuating said core portions with electric oscillations substantially throughoutv the speech frequency range for producing corresponding vibrations Aof said core portions across said two gaps so as to increase one gap while the other gap is decreased, a casing'for holding one of said core portions coupled under pressure to hearing inducing bones of the user outside the ear canal and carrying the other of said core portions in a floating condition with said casing, said floating core portion having a suiiiciently large mass and exerting under the action of the electricoscillations suflicient inertia reaction forces upon -said coupled core portion and therethrough upon the coupled bones for impartingvthereto the vibratory energy required for conducting corresponding vibrations through the bonesto the inner ear and induce intelligible hearing.

25.l In a bone conduction hearing device suitable for inc onspicuous wear by a user, a vibratory structure having a driving magnetic core member and a driven magnetic core member resiliently joined to form a magnetic flux path vincluding two gaps, said driven core member having a set of two surfaces on opposite sides of said driven core member forming pole faces for said two gaps,

said driving core member including core portions extending toward the pole faces of said driven core member to form the opposite pole faces of said two gaps. and windings interlinked with said flux path for actuating said core members with electric oscillations of the principal audible frequency range for producing corresponding vibrations of said core members across said two gaps so as to increase one gap while the other gap is A decreased, means including a rigid casing for holding said driven core member coupled under pressure to hearing inducing bones of the user outside the ear lcanal and carrying said driving core member in a floating condition within said' casing, said driving core member having a sumciently large mass and exerting under the action of the electric oscillations sufficient inertia reaction forces upon said driven core member and therethrough upon the coupled bones for imparting thereto the vibratory energy required for conducting corresponding vibrations through the bones to the inner ear and induce intelligible hearing. i

26. In a bone conduction hearing device suitable for inconspicuous wear by a user, a vibra.-

l tory structure having a driving magnetic core lses member and a driven magnetic core member resilientlyjoined to form a magnetic flux path including two gaps, said driven core member having a set of two surfaces on opposite sides of said driven core'rnember'formingN pole faces for'said" two gaps, said driving core member including core portions extending toward the pole faces of said driven core member to form the opposite pole faces of said two gaps, and windings interllnked with said flux path for actuating said core members with electric oscillations of the principal audible frequency range for producing corresponding vibrations of said core members across said twogaps so as to increase one gap while I the other gap is decreased, means including a casing for holding said driven core member coupled under pressure to hearing inducing bones of the user outside the ear canal and carrying said driving core member in a iloatng condition within said casing, saiddriving core member hav ing a mass sufficiently larger than the mass of said driven core member and exerting under the action of the electric oscillations suiiici'ent inertia reaction forces upon said driven core member and therethrough upon the coupled bones for imparting thereto the vibratory energy required for conducting corresponding vibrations through the bones to the inner ear and induce intelligible hearing, the stiffness of the resilient junction beresides in holding one core member coupled under g pressure against hearing inducingbones of the user so as to carry the other core member having a relatively large mass in a floating condition, and utilizing the floatingly carried core member `to exert vibratory inertia reaction forces upon the coupled core member and vtherethrough upon the bones for imparting thereto the vibratory energy required for conducting corresponding vibrations through the bones to the inner ear and induce intelligible hearing.

28. The method of inducing hearing with a vibratory hearing aid structure that vibrates under the action of electric oscillations of the audible frequency range, which resides in holding a vibratory portion of said structure coupled under pressure against hearing inducing bones of the user so as to carry the other vibratory portion of said structure having a relatively large mass in a floating condition, and utilizing the iioatingly carried vibratory portion to exert vibratory inertia reaction forces upon the coupled vibratory portion and therethrough upon the bones for impartinglthereto the vibratory energy required for conducting corresponding vibrations through the bones to the inner ear and induce intelligible hearing.

29. In a bone conduction hearing aid .device suitable for inconspicuous wear by a deafened person, an elastically deformable vibratory member having two vibratory portions and means for actuating said vibratory member with electric oscillations substantially throughout the speech frequency range for producing corresponding vibrations of said vibratory portions, one ofsaid vibratory portions having a contact surface -arranged to be held coupled under pressure to hearing inducing bones-of the user and iloatinglyV Icarrying the other of said vibratory portions, the floating vlbratory portion having sumcient mass and exerting under the action of the electric oscillations suiliclent inertia reaction forces upon the coupled vibratory portion and therethrough upon the coupled bones of the user for imparting thereto the vlbratory energy required for conducting corresponding vibrations through the bones to the inner ear of the user and induce intelligible hearing.

30. In a bone conduction hearing device suitable for inconspicuous wear by the user, an elastically deformable vibratory member comprising a driven vibratory portion having a contact surface element arranged to be held coupled under pressure to hearing inducing bones of the f user outside the ear canal and a driving vibratory portion iioatingly carried relatively to said contact surface portion, and means for actuating said vibratory member with electric oscillations of the principal audible frequency range to produce corresponding vibrations of said vibratory portions, said vibratory member and its bones to the inner ear of the user and induce therein intelligible hearing.

31. In a bone conduction hearing aid device suitable for inconspicuous wear by a deafened person, an elastically deformable vibratory member having two vibratory portions and means for actuating said vibratory member with electric oscillations substantially throughout the speech frequency range for producing corresponding vibrations of said vibratory portions, one of said vibratory portions having a rigidl contact surface element arranged to be held coupled under pressure to hearing inducing bones of the user outside theear canal and ioatingly carrying the other of said vibratory p ortions, said vibratory member and its several parts being so designed and proportioned thatat an overall size oi the vibratory member having a volume less than about two cubic inches, thel driving vibratory portion has a sufficiently large mass greater than about four grams and exerts under the action of the electric oscillations sufficient inertia reactionforces upon said rigid contact surface element and therethrough upon the coupled bones of the user for imparting thereto the vibratory energy required for conducting corresponding v ibrations through the bones to the inner ear of the user and induce intelligible hearing.

32. In a bone conduction hearing device suitable for inconspicuous wear by the user, a vibratory structure having two 'vibratory portions, means for actuating said vibratory structure with electric oscillations of the principal audible frequency range for producing corresponding vibrations between said vibratory portions, and means for holding one of said vibratory portions coupled under pressure to hearing inducing bones of the user outside the ear canal and carrying the other vibratory portion of said vibratory structure in a floating condition, said Boating vibratory portion having sufllcient mass and exerting under the action ci the electric oscillations sufficient inl ertia reaction for imparting to the coupled bones of the user the vibratory energy required for conducting corresponding vibrations through the bones to the inner ear of the user and induce intelligible hearing.

33. In a bone conduction hearing device suitable for inconspicuous wear by the user, a vibratory structure having one vibratory portion with a contact surface arranged for coupling under pressure to hearing inducing bones of the user and another vibratory portion iloatlngly carried by said bone coupled vibrator-y portion,

means for actuating said vibratory structure with electric oscillations of the principal audible Irequency `range for producing corresponding vibrations between said vibratory portions, the iloatingly carried vibratory portion having a mass suiliciently larger than the mass of said bone coupled vibratory portion and exerting under the action of the electric oscillations suicient inertia reaction forces upon the bone coupled vibratory portion and therethrough upon the bones `0f the user for imparting thereto the vibratory stantially throughout the speech frequency range I for producing corresponding vibrations of said vibratory portions, one of said vibratory portions having a rigid contact surface element arranged to be held coupled under pressure to hearing inducing bones of the user outside the ear canal and iloatingly carrying the other of said vibratory portions, said vibratory structure and. its several parts being so designed and proportioned that at an overall size of the vibratory member having a volume less than about three cubic inches, the driving vibratory portion has a sufciently large mass and exerts under the action of the electric oscillations sufficient inertia reaction forces upon said contact surface element and therethrough upon the coupled bones of the user i'or imparting thereto the vibratory energy required i'or conducting corresponding vibrations through the bones to the inner ear of the user and induce intelligible hearing, said bone coupled vibratory portion being arranged and shaped to protect said floating vibratory portion against external forces. 35. In a bone conduction hearing device suitable for inconspicious wear by the user, a vibratory structure having two vibratory portions, means for actuating said vibratory structure with electric oscillations of the principal audible frequency range for producing corresponding vibrations between said vibratory portions, and means for holding one of said vibratory portions coupled \vibratory energy required for conducting correspending vibrations through the bones to the inner ear of the user and induce intelligible hearing. said bone coupled vibratory portion being arranged and shaped to protect said iloating vi nbratoljy portion against external forces.

36. In a bone conduction hearing aid device suitable for inconspicuous wear by a deafened person, a vibratory structure having two vibratory portions and means for actuating said vibratory structure with electric oscillations substantially throughout the speech frequency range for v producing corresponding vibrations of said vibratory portions, one of said vibratory portions forming a casing having a contact surface arranged to be held coupled under pressure tohear ing inductlng -bones of the user, the other of said vibratory portions having suilicient mass and being ivloatingly 'carried withinl said casing so as to exert under the action of the electric oscillations suillcient inertia reaction forces upon the coupled vibratory portion and therethrough upon the coupled bones of the user for imparting thereto the vibratory energy required for conducting cor- CII responding vibrations through the bones to the inner ear of the user and induce intelligible hearing.

37. In an inconspicuous hearing imparting device, a vibratory structure comprising a rigid vibratory casing having an extended external vibration transmitting surface, a vibratory portion oatingly carried within said casing, means for actuating said vibratory structure with electric oscillations of the principal audible frequency range for producing corresponding vibrations between said tloatingly carried vibratory portion and said-casing, said iloatingly carried vibratory portion having surlicient mass -largerthan the mass of said casing andexert'ing under the action of the electric oscillations suincient inertia reaction forces upon saidl casing for imparting thereto vibratory energy required v for transmitting corresponding vibrations from the external surface of said casing tothe inner ear of the user and induce intelligible hearing.

38. In a bone conduction hearing device suitable for inconspicuous wear by the user, a vibratory structure comprising a driven'vibratory portion forming a part oi a rigid casing having a contact surface arranged to be held coupled under pressure to hearing inducing bones of the user outside the ear canal, a driving vibratory portion floatingly carried within said casing, and means for actuating said vibratory structure with electric oscillations oi the principal audible frequency range for producing corresponding vibrations between said vibratory portions,v said vibratory structure and its several parts being'v so designed and proportioned that at an overall size of the vibratory member having a volume less than about three cubic inches, the driving vibratory portion has a suiliciently large mass of the order of eight grams or more and exerts under the action of the electric oscillations suiicient inertia reaction forces upon said casing and therethrough upon the coupled bones of the user for imparting thereto the vibratory energy required for conducting corresponding vibrations through the bones to the inner ear of the user and induce intelligible hearing.

39. In a bone conduction hearing deviceY suitable for inconspicuous wear by the user, a vibratory structure having two vibratory portions, means for actuating said vibratory structure with electric oscillations of the principal audible fre'- quency range for producing corresponding vibrations between said vibratory portions, and a rigid casing for holding one of said vibratory portions coupled under pressure to hearing inducing bones of the user outside the ear canal and carrying the other vibratory portion of .said vibratory structure in a oating condition within said casing, said floating vibratory portion having sui- Acient mass and exerting under the action of the electric oscillations suiiicient inertia reaction forces upon said casing and therethrough upon the coupled bones lof the user for imparting thereto the vibratory energy required for conducting Corresponding vibrations through the bones to,the inner ear of the user and induce intelligible hearing,

40, In a -bone conduction hearing device suitable ior inconspicuous wear by the user, a vibraupon the casing and therethrough upon the bonesof the user for imparting thereto the vibratory energy required for conducting corresponding vlbrations through the bones to the inner ear of the user and induce intelligible hearing.

41. In a portable audiphone, the combination of electromagnetic means adapted toy respond to varying 4currents substantially throughout the audible frequency range, a relatively stiil vibrating member carrying the means and forming a narrow gap between the member and the means of ilxed dimension subject to the vibration imparted to the member by the means and which is lessin amplitude than-the width of the said air gap, and means for supporting the member in operative connection with the bone-structure of the user.

42. In a portable audiphone, the combination of a vibratory portion, an electromagnetic portion carried by said vibratory portion and including a speech coil andr adapted when the coil is energized by varying currents to effect vibration of said vibratory portion, said electromagnetic portion having greater inertia than said vibratory portion, and means for holding the vibratory portion in operative connection with the bone structure of the user, wherebythe vibrations of the vibratory portionare conducted through the bone structure to the inner ear of the user.

43. In a portable audiphone, the combination of a vibratory member, electromagnetic means carried by the member and adapted to respond to i varying currents substantially throughout` the audible frequency range for vibrating said member, and means for supporting the member in operative connection with the bone structure of the user, whereby the vibrations of said member are conducted through the bone structure to the inner ear of the user.

44. In a bone conduction hearing device suitable for inconspicuous wear by the user, a. vibratory unit comprising a driven vibratory magnetic core portion and a driving vibratory magnetic core portion having a resilient junction portion iioatingly carrying said driving core portion relatively -to said driven core portion so as to form therewith a magnetic ilux path including a magnetic gap, means including windings interlinked with said i'lux path for actuating said vibratory portions with electric oscillations of the principal audible frequency range to produce corresponding vibrations of said vibratory portions across said gap, and means including a substantially rigid casing enclosing said driving vibratory portion with its resilient junction portion and forming a part of said driven vibratory portion for holding said driven vibratory portion coupledunder pressure to hearing inducing bones of the user outside the ear canal', said vibratory unit and its several parts being so designed and proportioned that, at an overall size of the unit having a. volume of less than about three' cubic inches. the driving vibratory portion has a sum- 2o,s`oe

clently large mass and is subjected under the action of 'the electric oscillations to sufci'ent accelerations so that it exerts sufiicient inertia reaction forces upon said casing and therethrough upon the coupledbones of the user for imparting thereto the vibratory energy required for conducting corresponding vibrations through the bones to the inner ear of the user and induce intelligible hearing.

45. in a bone conduction hearing device suitable for inconspicuous wear by the user, a vibratory unit comprisingla driven vibratory magnetic core portion and a driving vibratory magnetic core portion having a resilient junction portion oatingly carrying said driving core. portion relatively to said driven core portion so as tov forming a part of said driven vibratory portion for holding said driven vibratory portion coupled under pressure tc hearing inducing bones of the user outside the ear canal, said vibratory unit and its several parts being so designed and proportioned that, at an overall size of the unit having a volume of less than about two cubic inches,

and a magnetic gap spacing of less than about ten thousandths of an inch, the driving vibratory portion has a. sufficiently large mass greater than about four grams and is subjected under the action of the electric oscillations to sufcient accelerations so that it exerts sumcient inertia reaction forces upon said casing and therethrough upon the coupled bones of the user for imparting thereto the vibratory energy required for conducting corresponding vibrations through the bones to the inner ear of the user and induce intelligible hearing.

46. In a bone conduction hearing device suitable for inconspicuous wear by the user, a vibratory unit comprising a. driven vibratory magnetic core portion and a. driving vibratory magnetic core portion having a resilient junction portion floatingly carrying said driving core portion relatively to said driven core portion so as to formtherewith a magnetic flux path including a magnetic gap, means including windings interlinked with said iiux path for actuating said vif bratory portions with electric oscillations o! the principal audible frequency rangetoproduce corresponding vlbrations of said vibratory portions across said gap, and means including a substantially rigid casing enclosing said driving vibratory portion with its resilient junction portion and forming a part of said driven vibratory portion for holding said driven vibratory portion coupled under pressure to hearing inducing bones of the user outside the ear canal, saidvibratory unit andv its several parts being so designed and proportioned that, at an overall size oi' the unit having a volume of less than about two cubic'inches. and a magnetic gap spacing securing good operating etliclency, the driving vibratory portion has' a sumciently large mass o! the order of eight gramsor more/and'is subjected under the action ofthe electric oscillations to suiclent accelerations so thatit exerts sumcient inertia reaction forces uponsaid ,casing and therethrough upon the coupled bones of the user for imparting thereto the vibratory energy required for conducting corresponding vibrations through the bones to the inner ear of the user and induce intelligible hearing.

47. In a bone conduction hearing device 'suitable for inconspicuous Wear by the user, a vibratory unit comprising a driven vibratory magnetic core portion and a driving vibratory magnetic core portion having a, resilient junction portion iloatingly carrying said driving core portion relatively to said driven core portion so as to form therewith a magnetic iiux path including a magnetic gap, means including windings interlinked with said flux path for actuating said vibratory portions with electric oscillations of the principal audible frequency range to produce correspending vibrations of said vibratory portions.

across said gap, and means including a substantially rigid contact surface element arranged and shaped to protect said driving vibratory portion with its resilient junction portionragainst external forces and forming a part of said driven vibratory portion for holding said driven vibratory portion coupled under pressure to hearing inducing bones of the user outside the ear canal, said vibratory unit and its several parts being so designed and proportioned that, at. an overallsize of the unit having a volume of less than about three cubic inches, the driving vibrato7 portion has a sufficiently large mass of the order of eight grams or more and is subjected'under the action of the electricv oscillations to suilicient accelerations so that it exertssuiiicient inertia reaction forces upon said contact surface element and 'therethrough upon the coupled bones of the user for imparting' thereto the vibratory energy required for conducting corresponding vibrations `through the bones to the inner ear of the user and induce intelligible hearing.

mi 48. In a .bone conduction hearing device suitable for inconspicuous wearby the user, a vibratory unit comprising a. driven vibratory portion and a driving vibratory portion having a resilient junction portion floatingly carrying said driving vibratory portion relatively to said driven vibratory portion. means for actuating said vibratory portions with electric oscillations oi the principal audible frequency range to produce cor-- responding 'vibrations of said vibratory portions, and means including a. substantially rigid casing enclosing said driving vibratory portion with its hearing.

resilient junction portion and forming a part of said driven vibratory portion for holding said driven vibratory portion coupled under pressure to hearing inducing bones i theuser outside the ear canal, said vibratory unit and its several parts being so designed and proportioned that, at an overall size of the unit. having a volume of less than about three cubic inches, the driving vibratory portion has a sufliciently large mass greater than about four gramsand is subjected under the action of the electric oscillations to suicient accelerations so that it exerts sufficient inertia reaction forces upon said casing and therethrough upon the coupled bones of the user for imparting thereto the vibratory energy required for conducting corresponding vibrations through the bones to the inner ear of the user and induce intelligible hearing. y

49. In a bone conduction hearing-device suitable for inconspicuous wear by the user, a vibratory unit comprising a driven vibratory por-- ing a. part of said driven vibratory portion for holding saiddriven vvibratory portion coupled under pressure to hearing inducing bones of the user outside the ear canal, said vibratory unit and its several parts being so designed and proportioned that, at an overall size of the unit having a volume of less than about two cubic inches, the 'driving vibratory portion has a sufliciently large mass of the order of eight grams or more and is subjected under the action of the electric oscillations to suihcient accelerations so that it exerts suiiicient inertia reaction forces upon said contact surface element and therethrough upon the coupled bones of the user for imparting theret'o the vibratory energy required for conducting corresponding vibrations through the bones to the inner ear of the user and induce intelligible mm. HENRY GREIBACH. 5 

